How to control the temperature and pressure of PE plastic to ensure product quality during processing?
Release Time : 2025-03-12
In the processing of PE plastic (polyethylene plastic), temperature and pressure are two crucial control parameters. They directly affect the melting state, fluidity, molding effect and quality of the final product of PE plastic. Therefore, scientific and reasonable control of processing temperature and pressure is the key to ensure the quality of PE plastic products.
1. Temperature control strategy
The processing temperature of PE plastic usually needs to be determined according to its density and melt flow rate (MFR). Generally speaking, the processing temperature of LDPE (low-density polyethylene) is relatively low, about between 110℃ and 180℃; while the processing temperature of HDPE (high-density polyethylene) is relatively high, about between 180℃ and 220℃.
Preheating and melting: Before the processing begins, the PE plastic raw material needs to be preheated to a certain softening temperature to facilitate subsequent melting and extrusion. The preheating temperature should be gradually increased to avoid rapid heating that causes the plastic to burn or decompose.
Barrel temperature zone control: The barrel of an injection molding machine or extruder is usually divided into multiple heating zones, and the temperature of each zone can be independently adjusted according to the melting state and flow of the plastic. Generally speaking, the barrel temperature should be gradually increased from the feed port to the nozzle to ensure that the plastic is evenly melted and has good fluidity.
Mold temperature control: Mold temperature has an important influence on the crystallinity and molding effect of PE plastic. Higher mold temperature can promote the crystallization of plastics and improve the strength and toughness of products; but too high mold temperature may also cause the shrinkage rate of products to increase or generate internal stress. Therefore, it is necessary to set the appropriate mold temperature according to the specific requirements of the product.
2. Pressure control strategy
In the processing of PE plastic, pressure mainly includes plasticizing pressure and injection pressure.
Plasticizing pressure (back pressure): Plasticizing pressure refers to the pressure on the top of the screw when the screw rotates backward in a screw injection machine. Appropriate plasticizing pressure helps to uniform the melt temperature, uniformly mix the colorant, and discharge the gas. However, too high plasticizing pressure may cause the melt temperature to rise too quickly or even burn; while too low plasticizing pressure may cause uneven melt temperature or incomplete melting of the plastic. Therefore, it is necessary to set the appropriate plasticizing pressure according to the type of plastic and processing requirements.
Injection pressure: Injection pressure is one of the key parameters in the injection molding process, which determines whether the melt can smoothly fill the mold cavity and form a good product. The size of the injection pressure depends on factors such as the fluidity of the melt, the wall thickness and shape of the product. Generally speaking, for PE plastic with good fluidity, a lower injection pressure can be used; while for thin-walled, long-flow or complex-shaped products, the injection pressure needs to be appropriately increased to ensure the integrity and dimensional accuracy of the product.
3. Comprehensive control strategy
In the processing of PE plastic, the control of temperature and pressure is interrelated. Too high or too low temperature may lead to unstable pressure, which in turn affects the quality of the product. Therefore, in actual operation, it is necessary to comprehensively adjust the temperature and pressure parameters according to the type of plastic, processing requirements and equipment performance. At the same time, it is also necessary to pay close attention to various changes in the processing process, such as the flow state of the melt, the appearance quality of the product, etc., so as to adjust the control strategy in time to ensure the stability and consistency of the product.
In summary, scientific and reasonable control of processing temperature and pressure is the key to ensuring the quality of PE plastic products. By continuously optimizing the control strategy, processing efficiency can be improved, production costs can be reduced, and the market competitiveness of products can be enhanced.
1. Temperature control strategy
The processing temperature of PE plastic usually needs to be determined according to its density and melt flow rate (MFR). Generally speaking, the processing temperature of LDPE (low-density polyethylene) is relatively low, about between 110℃ and 180℃; while the processing temperature of HDPE (high-density polyethylene) is relatively high, about between 180℃ and 220℃.
Preheating and melting: Before the processing begins, the PE plastic raw material needs to be preheated to a certain softening temperature to facilitate subsequent melting and extrusion. The preheating temperature should be gradually increased to avoid rapid heating that causes the plastic to burn or decompose.
Barrel temperature zone control: The barrel of an injection molding machine or extruder is usually divided into multiple heating zones, and the temperature of each zone can be independently adjusted according to the melting state and flow of the plastic. Generally speaking, the barrel temperature should be gradually increased from the feed port to the nozzle to ensure that the plastic is evenly melted and has good fluidity.
Mold temperature control: Mold temperature has an important influence on the crystallinity and molding effect of PE plastic. Higher mold temperature can promote the crystallization of plastics and improve the strength and toughness of products; but too high mold temperature may also cause the shrinkage rate of products to increase or generate internal stress. Therefore, it is necessary to set the appropriate mold temperature according to the specific requirements of the product.
2. Pressure control strategy
In the processing of PE plastic, pressure mainly includes plasticizing pressure and injection pressure.
Plasticizing pressure (back pressure): Plasticizing pressure refers to the pressure on the top of the screw when the screw rotates backward in a screw injection machine. Appropriate plasticizing pressure helps to uniform the melt temperature, uniformly mix the colorant, and discharge the gas. However, too high plasticizing pressure may cause the melt temperature to rise too quickly or even burn; while too low plasticizing pressure may cause uneven melt temperature or incomplete melting of the plastic. Therefore, it is necessary to set the appropriate plasticizing pressure according to the type of plastic and processing requirements.
Injection pressure: Injection pressure is one of the key parameters in the injection molding process, which determines whether the melt can smoothly fill the mold cavity and form a good product. The size of the injection pressure depends on factors such as the fluidity of the melt, the wall thickness and shape of the product. Generally speaking, for PE plastic with good fluidity, a lower injection pressure can be used; while for thin-walled, long-flow or complex-shaped products, the injection pressure needs to be appropriately increased to ensure the integrity and dimensional accuracy of the product.
3. Comprehensive control strategy
In the processing of PE plastic, the control of temperature and pressure is interrelated. Too high or too low temperature may lead to unstable pressure, which in turn affects the quality of the product. Therefore, in actual operation, it is necessary to comprehensively adjust the temperature and pressure parameters according to the type of plastic, processing requirements and equipment performance. At the same time, it is also necessary to pay close attention to various changes in the processing process, such as the flow state of the melt, the appearance quality of the product, etc., so as to adjust the control strategy in time to ensure the stability and consistency of the product.
In summary, scientific and reasonable control of processing temperature and pressure is the key to ensuring the quality of PE plastic products. By continuously optimizing the control strategy, processing efficiency can be improved, production costs can be reduced, and the market competitiveness of products can be enhanced.